Each of the Big Three U.S. automakers said Thursday they will idle assembly plants next week, a sign that demand for some car models is still sluggish.

In the biggest single week of down-time this year, General Motors Corp. will idle two car plants and curtail production at a third, Ford Motor Co. will idle two car plants and Chrysler Corp. will idle one plant.

The actions are expected to place more than 12,000 auto workers on temporary layoff next week.

The automakers all said the shutdowns were aimed a reducing dealer inventories, which have swelled in recent months as higher interest rates dampened demand.

Ford said it plans to idle its plants in Wayne, Mich., which builds Ford Escort small cars and in Lorain, Ohio, which builds the Ford Thunderbird and Mercury Cougar coupes.

GM said it will idle its car plants in Oklahoma City, which builds Oldsmobile Ciera and Buick Century sedans and wagons, and in Doraville, Ga., which builds Cutlass Supreme sedans and coupes.

GM also will cut back production at its Cadillac luxury car assembly plant in Hamtramck, Mich., to a single shift.

Chrysler will idle its Newark, Del., car assembly plant next week to adjust inventories of the LH sedans built there, the Dodge Intrepid and Chrysler Concorde.

According to Automotive News, dealer inventories of nearly all of the affected cars were close to or above 100 days worth of supply.

Chrysler said Thursday it was extending rebates ranging from $300 to $2,000 on several left-over 1994 models and slow-selling 1995 models through June 30.

The "Customer Preferred Savings" program, which was scheduled to expire March 31, offers a $750 rebate on the 1994 Eagle Talon, $1,500 on Dodge Spirit, Plymouth Acclaim and Chrysler LeBaron sedans and $300 on 1994 Jeep Wrangler four-cylinder models, the company said. It also offers $2,000 on 1994 Dodge Ram Wagon, Ram Van and conversion vans and $500 on 1995 versions of those same models, excluding B-150 short wheelbase vans.

It will continue to offer rebates of $400 to $600 on its Neon models, up to $1,500 on its minivans for repeat buyers and up $1,500 on its LH sedan models.